This invention relates to an electroless plating process and formulations and, more particularly, to an electroless plating process for depositing gold on a substrate with a formulation that has such stability that spontaneous deposition cannot occur.
In the processing of electronic components, electroless gold has been used to achieve uniform metal distribution as well as deposition onto areas that are not in contact electrically.
Much has been described in literature comparing immersion (or displacement) processes with electroless (or autocatalytic) techniques. In summary, immersion systems will produce a maximum coating thickness of about 1/4 to 1/2 micrometer whereas electroless systems have no limit to thickness except that which is practical--for gold, about 2 to 4 micrometers.
The prior art discloses many processes for the production of gold coatings to appreciable thicknesses; the outstanding two are:
1) U.S. Pat. No. 3,396,042--catalytic reduction and
2) U.S. Pat. No. 3,798,056--borohydride reduction.
Although these processes can produce satisfactory gold deposits, they are unstable for long term production in high volume manufacturing operations. The stability of the gold complex is lowered by the chemistry utilized and total system decomposition occurs.